The present invention relates generally to an intracardiac potential analyzing apparatus and method in electrophysiologic cardiography using a computer, and more particularly to an apparatus and method for analyzing an excitation propagation path for an arrhythmia of reentry type (atrial tachycardia, atrial flutter, atrial fibrillation, ventricular tachycardia, ventricular fibrillation, or the like).
The arrhythmias are generally classified into three according to their mechanisms: abnormal automaticity, reentry, and triggered activity.
Arrhythmias due to abnormal automaticity and triggered activity may be understood to be arrhythmias in which an excitation wave generated at a certain site extends within the heart and reaches a boundary or collides with another excitation wave propagating through a different path to eventually extinguish without returning to the original site. An arrythmia due to reentry, in turn, may be understood to be an arrythmia that is maintained by an excitation wave passing a certain site, which propagates through the heart and returns to the same site.
At present, a method called isochronography is used for the analysis of intracardiac excitation propagation. The isochronography represents how excitation has propagated by defining a certain time as a reference start time, and connecting with lines exciting sites at a time a certain period of time after the start time. This is exactly the same as contour lines used in maps. The isochronography may be useful for analyzing an arrythmia which may be understood as an image in which the arrythmia has started at a peak, and excitation propagates toward the base, i.e., useful for arrhythmias which involve abnormal automaticity and triggered activity as their mechanisms. Stated another way, the isochronography is useful for an arrythmia that has a pattern in which excitation starts at a certain time and ends at another time.
An arrythmia due to reentry, however, is established by excitation repetitively turning about a circuit, so that it is not possible to specify the start or the end of the excitation. Specifically, in this type of arrythmia, excitation is present anywhere without fail before a certain time, and if the excitation is traced backwardly, the path of the excitation returns to the original site. If a start time and an end time are forcibly set for conducting the isochronographic analysis, different analysis results will be produced depending on where the start time and end time are set. FIGS. 15A, 15B illustrate an example of the results produced from such an analysis. Specifically, FIGS. 15A, 15B are exemplary diagrams which have been created by setting different excitation start times T1, T2 in an electrocardiogram of FIG. 2. As is apparent from these diagrams, different results are produced when different start times are set.
Thus, the establishment of analytical technologies has long been desired for facilitating estimation of an intracardiac excitation propagation path of an arrythmia due to reentry.
The intracardiac excitation propagation may be understood just as the propagation of waves since excitation at a certain site causes excitation at an adjacent site. The intracardiac excitation propagation, however, differs from waves propagating the surface of water in that a wave cannot pass a site which has once been passed by another wave for a certain period of time. (After a myocardial tissue has excited, there is a period of time called the xe2x80x9crefractory periodxe2x80x9d in which the myocardium cannot excite.) Therefore, phenomena such as reflection and overlapping are not found in the intracardiac excitation propagation. Specifically, a wave caused by an exciting myocardial tissue disappears when it reaches a boundary of the myocardial tissue, for example, the boundary between an atrium and a vein or the boundary between an atrium and a ventricle. In addition, when excitation waves collide with each other, they also disappear. Thus, the excitation propagation may be processed as an excitation wave which has such characteristics as mentioned above.
The present invention intends to know the nature of a progressing excitation wave by analyzing the excitation wave on the assumption that an excitation wave linearly progresses within a sufficiently small region. The progressing speed and progressing direction of a linearly progressing wave can be derived by measuring times at which the progressing wave, i.e., the excitation wave passes three different electrodes at known positions and calculating them from the measured values. Thus, the present invention calculates the progressing direction and speed of an excitation wave front for an arrythmia based on time differences (hereinafter called the xe2x80x9cexcitation wave passing timexe2x80x9d) between a reference time arbitrarily set on an electrocardiogram and times at which the excitation wave passes bipolar electrodes existing at three points within a region sufficiently small to assume that the progressing direction of the excitation wave will not change, and further based on positional information on the three bipolar electrodes, and represents an intracardiac excitation propagation by displaying it as vectors, thereby facilitating estimation of an intracardiac excitation propagation path for an arrythmia due to reentry.
The present invention can represent an intracardiac excitation propagation path with sets of vectors indicative of progressing directions and progressing speeds of local excitation waves without being affected at all by a start time and an end time of excitation. Since excitation wave vectors are calculated on the basis of time differences at respective excitation points, the representation of the intracardiac excitation propagation path will not either be affected by the position of a reference time which is set on an electrocardiogram for measuring excitation wave passing times. This results in facilitating diagnosis and treatment of a variety of arrhythmias, mainly those due to reentry. Further, by virtue of the direct representation of the progressing directions and progressing speeds of excitation waves as vectors, the present invention facilitates estimation of the mechanism involved in an arrhythmias.